Method and apparatus for determining the gelation temperature of solutions capable of gelling



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C. FORDYC AND APPARA 5 FOR DET PERATURE OF SOLUTIONS CA Filed Sept. 11

METHOD TEM Patented Dec. 7, 1943 METHOD AND APPARATUS FOR DETERMIN- ING THE GELATION TEMPERATURE OF SOLUTIONS CAPABLE OF GELLING Charles R. Fordyce and Harold F; Vivian, Rochester, N. Y., assignors. to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application September 11, 1941, Serial No. 410,426

11 Claims.

The present invention relates to a method and apparatus for rapidly and accurately determining the gelation temperature of a liquid solution capable of gelling.

It has been common practice for some time in the art of formin thin sheeting and film base to spread a thin coating of a desired material, generally a solution of a cellulose ester, such as cellulose acetate, in a suitable solvent, onto a heated surface and cause the solvent to evapocompleted revolution sufiicient solvent has been removed from the solution so that the sheet resulting can be stripped from the wheel and conveyed to awind-up, or carried over other rolls or drums for further curing treatment.

Recently, solutions or dopes known as gel dope have been made known for forming sheets in the manner set forth. These gel dopes differ from those previously used in that they are fluid above a given gelation temperature, but become a gel at or below said gelation temperature without any appreciable loss in solvent. With gel dopes a cold wheel, i. e., one which is below the gelation temperature of the dope, is used in place of a hot one and the gelled strip is capable of being stripped from the surface of the wheel in sheet form. The present invention will perhaps be better understood if the characteristics and nature of a gel dope are explained. These gel dopes may be formed by dissolving at elevated temperature or moderately elevated temperature certain cellulose organic esters such as cellulose acetate propionate and cellulose acetate butyrate and the like in a solvent mixture consisting of propylene chloride and ethylene chloride, or propylene chloride and a lower aliphatic alcohol such as methyl alcohol, to give solutions or dopes which are susceptible of gelation by a rapid lowering of temperature. I

original solvent. In short, this type of fluid can be maintained as a fiuid at temperatures between 10-50 degrees C. and when allowed to cool to or below a critical temperature between 10 C.- 40" 0., depending on the composition, form transparent gels which remain homogeneous through out the gelling operation. When the gels are first formed they do not adhere strongly to the cooled film-forming surface and although the gel itself contains a relatively large amount of solvent, i. e., an amount of solvent equal to or greater than the weight of the cellulose ester, it is sufficiently strong and resistant to deformation so that it can be continuously stripped fromjhe coating wheel. Upon leaving the wheel, the gel-like film is usually further dried to reduce the solvent content to a minimum. A complete disclosure of a typical gel dope is made in U. S. patent application Serial No. 245,023, filed December 10, 1938, in the names of Charles R. Fordyce and Austin J. Gould. However, it is pointed out that this gel dope is given only as one illustration of the type of solution which the present method and apparatus is used to determine the gelation temperature of, and that thepresent method and apparatus can be used to determine the gelation temperature of any solution which is fiuid above a given gelation temperature and is capable of gelling when reduce in temperature to, or below, said given gelation temperature, regardless of the composition of the solution or its use subsequent to gelling.

Inasmuch as the gelation temperature of a solution, or dope, of the type set forth will vary with its composition, it will be readily apparent to those skilled in the art that it is important that some method and means be available for accurately determining the gelation temperature .of a solution in a rapid and consistently reproducible manner. This determination is necessary to attain adequate production control so thatfall batches of solution can be made uniform, or to have the same gelation temperature. The operating characteristics of the casting wheel may determine the gelation temperature to be used, whereby the solution is made up to possess such a gelation temperature; or the coating wheel may be adjusted to be suitable for the gelation temperature of a solution, or dope, found to have desirable characteristics. Whether the composition of the solution is varied to give a gelation temperature determined by the operating characteristics of the wheel, or vice versa, the fact remains that it is necessary in production control to be able to obtain in a rapid reproducible manner the gelation temperature of a given solution. In addition to determining the gelation temperature of a given dope, or solution, it is desirable to know the stripping characteristics of such a dope upon gelling. V V V g It is not only desirable to know the gelation temperature of solutions of the type set forth, but it may be equally desirable to know the gelation temperature of an aqueous solution of gela- T tine commonly used as a coating material. Aquee ous solutions of gelatine possess the property of being fluid above a certain temperature at which they gel and this gelling property is advantageously used in the coating of suchsolutions, the solution being applied while in a liquid form and gelled by chilling after application. With coatings of gelatine solutions it is necessary to know the gelation temperature of the same so that the chilling apparatus can be adjusted in accordance therewith, or vice versa. Furthermore,.since the gelation temperature of a, gelatine solution depends upon at least three variables, concentration, age, and pH of the solution, it is'necess'ary that it be possible to readily obtain the gelation temperature of such a solution for the purpose of production control.

Therefore, the primary object of the present invention is the provision of a method of determining in a rapid and reproducible manner the gelation temperature of a liquid solution capable of gelling at a given temperature or .within a given temperature range.

Another object is the provision of a method of determining the gelation temperature of a liquid solution capable of gelling at a given temperature which also indicates the stripping characteristics of the solution after gelling.

A further object is the provision of a method of the type set forth which can be carried out in a rapid and reproducible manner suitable for production control of said solution. 7

And yet another object is the provision of an apparatus for carrying out the method above set forth, and which apparatus is simple to use, cheap to manufacture, and efficient in operation.

Briefly, the method constituting the present invention comprises the steps of applying a uniform strip of the solution to be'tested in liquid form along a support having a temperature gradient including the gelation temperature of the solution, allowing aid deposited strip to remain on said support for a given time, determining the point on the support at which the deposited strip ceases to be a fluid and. becomes a'gel, and noting the temperature of the support at said 'method of operation, together with additional objects and advantages thereof, will best be un- -de'rstood from the following description of specific embodiments when read in connection with the accompanying drawing in which,

Fig. 1 is a perspective View of an apparatus constructed inaccordance with a preferred embodiment of the present invention for determining the gelation temperature of a gel dope, and showing a dispenser for the dope attached to the apparatus in operative position,

Fig; 2 is aplan view of the apparatus shown in Fig. 1, and showing the ends of the test bar immersed in water condensers for creating the desired temperature gradient along the'bar,

Fig. 3 is a sectional view taken substantially on line 33 of Fig. 2,

Fig. 4 is an enlarged partial section of the test bar with the slide removed, and showing the form of test strip of gel dope which is deposited thereon by the slide,

Fig. 5 is a sectional view corresponding to Fig. 3, but showing the form of groove and slide suitable for use in testing aqueous solutions of gelatine,

Fig. 6 is an enlarged partial section of the test bar shown in Fig. 5, and showing the form of test strip suitable with aqueous solutions of gelatine or solutions which are not susceptible to being readily stripped from the bar, and

Fig. I is anelevational view of a comb adapted to be drawn laterally of a test strip of a gelatine solution for determining the point in said strip where the solution ceases to be a fluid and becomes agel.

Like reference characters refer to corresponding parts throughout the drawing.

In the use of solutions of cellulose acetate or other dopes which form gels upon cooling, it is necessary to know the temperature of gelling. Previously it has been proposed to, determine the gelation temperature by immersing'a bottle of the solution, or dope, in a controlled cooling bath and observing the temperature at which the gelation took place. It is customary in the use of these dopes, or solutions, to cast them in liquid form upon a metal surface coded below the gelation temperature of the solution; and to strip the gelled solution from the surface. By the above noted bottle method ofdetermining the gelation temperature, the coating properties such as temperature of gelling, stickiness, and heat of coating on metal are not determined.

In accordance with our method of determining the gelation temperature of a liquid solution capable of gelling at a given temperature, the solution in liquid form, and at the temperature of coating, is applied in a uniform strip along a support having a temperature gradient including the gelation temperature. The deposited strip of solution is then allowed to remain on the sup- ,port for a given time until the mass of solution has attained the temperature of that part of the support it is deposited upon. Then the point in the strip where the solution ceases to be a fluid and becomes a gel is determined in a suitable way, as will be hereinafter set forth, and the temperature of the support at this point is determined and assumed to be the gelation temperature of the solution under test. With solutions of the gel dope type which include solvents, the strip upon gelation of the solution is strong enough to allow it to be stripped from the lower temperature end of the bar toward the higher temperature end to determine the point at which the same first tends to stick to the sup v por point is then determined and assumed to be the Thetemperature of the support at this jgelation temperature of the. solution. We have found, however, that gelatine solutions upon gelling may not possess sufficient strength to permit stripping from. the test. bar without accidental rupture even at points therealong where gelation is complete, so that with solutions of this type a method of determining the gelation point on. the bar other than stripping from the bar is generally utilized as will be hereinafter fully set means may be provided for heating one. end of the bar and cooling, the other end thereof to provide a desired temperature gradient along the length of the same. As an example of a simple and efiicient means for doing this we have shown the ends of the bar terminating in circular ends I 3 and M, the end l3. being immersed in a hot water condenser l6 and the end M being immersed in a cold water condenser ii. The temperature of the water in the two condensers may be readily controlled to give any desired temperature gradient along. the bar.

After the bar temperatures come to equilibrium a uniform strip of the solution is coated along the top surface ll of the bar so that the groove I2 is filled with the solution. When testing solutions which include solvents it has been found necessary to protect the solution in the groove with a top strip H, (see Fig. 4) to prevent evaporation of the solvents and curing of that portion of the solution in the groove due to the evaporation of the solvents. If the groove were merely filled with solutions, solvents would. evaporate therefrom and the gelling of the solution would be effected by curing and a true gelation temperature would not be obtained. The top strip I1 is formed over the groove I2 by depositing a surplus of solution on the surface of the bar and confining this surplus in a suitable manner to provide a strip of solution of the desired thickness on the surface If on the, bar in covering relation to the solution in the groove.

One suitable means of depositing the test solution on the bar in a manner to fill the groove with the solution and provide a protective top strip thereover is by use of the slide 2b. This slide, as shown, may comprise a U-shaped block .of any suitable-material the inside faces of side arms 2| of which engage side walls 22 of the bar .to prevent movement of the slide laterally of the bar. The face of the cross member 23 of the slide adjacent the top of the bar is provided with an elongated recess 24 disposed directly above the groove in the bar and the depth and Width of this recess determines the width and thickness of the top strip of solution formed over the tube is forced from the tube and into the recess 24 and from there into the groove I 2. When it is desired to deposit a test strip'on the bar, the slide is moved from the warm end of the bartoward the cold end thereof at the same time the dispensing tube is being squeezed, with the result that a proper test strip of dope is deposited on the top surface of the bar, said test strip including a column of solution in the groove and covered by a top strip of desired proportion. In other words, the recess 24 in the slide acts to form a small column of solution in the groove I2 protected from curing by the top strip to give a true gelation temperature.

After a given waiting time, which is determined in the manner hereinafter set forth, said test strip is stripped from the bar starting at the lower temperature end thereof. This stripping action is continued at a uniform rate until the column of. dope in the groove sticks to the support. This point of sticking is noted and the temperature of the bar at this point is determined and is the gelation temperature of the dope, or the temperature at which the solution ceases to be a fluid and. becomes a gel strong enough to permit stripping. The temperature of any point on the bar could be determined in any suitable manner, i. c. with a copper constantin thermocouple and a Leeds and Northrup Type K potentiometer. However, in order to give a simple and rapid measurement of temperature at any point along the bar merely by inspection We have found that it is desirable to drill a number of holes 29 into the bar at spaced equal intervals along its length and imbed thermometers 30 in these holes with nickel paste. That side of the bar into which the thermometers are adapted to be inserted is provided with an enlarged portion 41 to provide ample support for the thermometers when inserted into the bar, as will be obvious from an inspection of Fig. 3. These thermometers will permit one to directly read the temperature at any point along the bar to the nearest half degree of the point at which the test strip sticks in the bar groove l2 and will serve to inform the operator when the bar test strip is in equilibrium when starting a test.

We have found that the gelation temperature, or really the point of sticking, taken for a series of waiting times, will be the same for a period of several minutes if the top strip thickness is correct. For example, tests made with a solution which will be referred to as A, and comprising one part by weight of a cellulose acetate butyrate containing 16% by weight butyryl, and 32% by weight acetyl dissolved in 4 parts by Weight of a solvent mixture composed of 25% by weight of ethylene chloride, and 75% by weight of propylene chloride and containing triphenyl phosphate equal to 7% of the weight of the cellulose ester, gave the following Waiting time-temperature, reactions.

Temper- Walting hme m i F. 1 minute 2 minutes 4 minutes. 6 minutes. 7 minutes. 8 minutes" 10 minutes .l

:p'ossible'as it indicates a period of stability.' If

the top strip coated on the bar is not thick enough This indicates that the tion inthe groove l2 and that curing due to the evaporation of the solvents is influencing the gellingof the solution rather than having a gel condition influenced by temperature alone.

After a proper top strip thickness has been obtained for'any given solution a further thickness increase has little effect. A maximum lowering of 2 F. in the measured temperature was observed for more than a 50 per cent increase in the top strip thickness of solution A above noted, and the plateau effect still persisted. The plateau effect may be used to advantage when testing the application of an unknown solution to the stripping bar. If the plateau effect is obtained, the top strip thickness on the bar is satisfactory for obtaining reproducible results using one of the waiting times giving the plateau temperature.

We have found that the proper top strip thickness for different solutions varies with the composition of the solution. For example, with a solution which we will refer to as B and comprising one part by weight of a cellulose acetate bu- 'gave the following results with this test:

I. 4:1 solvent ratio; X-7% of weight of butyrate- Waiting time vs. gelation temperature acetate g Per cent 6 min. 7 min. 8 min. 9 min.

' F. F. F. F. 20 80 79 78 80 82 25 75 74 74 74 75 27 73 74 74 75 74 3O 70 69 69 70 7.1 33 67 66 68 68 63 II. 4:1 solvent ratio; X7% of weight of acetate butyrate Waiting time vs. gelation temperature Permnt g f 2 min. 3min. 4 min. min.

F. F. F. F. 65 25 77 78 78 79 66 24 1O 73. 5 74 74 76 67 23 10 69 69 7O 85 68 22 10 66 66 68 69 69 21 10 58 6O 6O 61 71 19 1O 56 V 57 57 60 Y-Ethylene chloride Z-Propylene chloride 'X-Triphemrl phosphate UCyclo hexane V-Butyl alcohol By referring to the above noted table it will be apparent that-the gelation temperature of a solution of the type set forth varies with the composition of the solution. It will, therefore, be readily appreciated by one skilled in the art how the determination of the gelation temperature of such a solution serves as an accurate and rapid means of checking the production of different batches of a given solution tobe sure that they are all the same or meet the coating conditions available with a given coating apparatus.

The investigation of this method of determining the gelation temperatures of solutions capable of gelling at a given temperature has been found to give reproducible results under conditions which ar not critical. The waiting time and top strip thickness, while they have certain minimum values, mayb varied quite a bit over these values. There is only one objection to having a top strip which is too thick to sufiiciently isolate the column of solution in the groove so that it wont be affected by the evaporation of solvents. This is found to be that if the top strip is too thick it will not sufficiently cure during the waiting time to permit it to be readily stripped from the top of the bar with the result that it is liable to stick and hinder the test column of solution from being readily and uniformly stripped from the groove. If the top strip is not too much in excess of the necessary thickness to serve its purpose of isolating the column of solution in the groove and bar, it will be sufliciently cured'during the desired waiting time so that it will readily strip from the surface H of the bar and not hinder proper stripping of the test column of solution from the groove It.

With this method and apparatus a number of solutions of similar types that have widely varying gelation temperatures may be measured by using the same waiting time. It is necessary,

' however, to distinguish between solutions of different composition, as the waiting times of solutions A and B above noted are difierent. Unknown solutions may be adapted to this method by varying the top strip thickness until a plateau efiect is obtained whereby reproducible results will be insured. The testing bar may be made of the same material as the surface over which the solution is to be passed so that the bar in addition to serving in its capacity of determining the gelation temperature of the solution will give an indication of the stripping characteristics of a solution when applied to the casting surface. The coating wheel or casting surface, must be just slightly colder than the gelation temperature determined on the test bar in order to obtain clean stripping. The gelation temperature obtained by the noted bottle method does not have this significance since a solution cannot be stripped from a wheel whose temperature is just below the gelation temperature indicated by this bottle method.

The question might be asked as to why the temperature of the coating wheel could not be made so low as to be sure any solution deposited thereon would be sure to gel instead of going to the trouble of determining the gelation temperature of the solution, or the highest temperature at which the solution would change from a fluid to a gel strong enough to permit stripping.

-It has been found that the physical characteristics of a sheet formed from such a solution are the best when cast onto a coating Wheel the temperature of which is just below the gelation temaeeazes perature of'the solution. If the solutionis gelled too severely, or quickly, the sheet so formed has been found to present poor tear quality, or tends to shatter rather than tear. Furthermore, if the solution is too quickly cooled the solution has no chance to even itself on the coating wheel with the result that a sheet of irregular thickness results.

When the solutions being tested were aqueous solutions of gelatine it was found that the gelled test strip of such a solution did not always possess suflicient strength to permit the same to be stripped from the bar, and often tended tobreak, even in the portions which were completely gelled. T-o adapt the present method and apparatus to the determination of the gelation temperature of aqueous solutions of gelatine a test bar like the one used in testing the solution containing solvents was used but the groove l2 in the top surface thereof was made relatively shallow and wide compared to that used for testing the solution capable of being stripped when gelled. The gelatine solution could be applied to the groove l2 by the use of the slide as in the previously described method, but the slide need have no definitely shaped recess above the slot in the bar because no top strip is needed over the solution in the groove. The top strip can be eliminated when testing aqueous gelatine solutions because water will not evaporate from the gelatine solution enough to affect the gelling of the solution.

After the deposited gelatine solution has remained on the test bar for a given time the pins 3| of a comb 32 (see Fig. 7), are pressed into one edge of the test strip and the comb is moved laterally of the strip. The comb is made equal in length to the test bar and the pins thereon re spaced at regular intervals so that a number of points in the test strip may be simultaneously tested at one time. In the firm hard gelatine of the strip the grooves made by the pins of the comb are clear out, while in the soft gel ragged and sloppy edges are formed, and in the liquid there is little or no change because the fluid fills in behind the pins as fast as they move across the test strip. The temperature of the bar as read on the thermometers under these divisions is observed and recorded as a gel temperature. Although a test strip of an aqueous solution of gelatine requires no top strip, for the reasons set forth above, it was found that when the under surface of the cross member 23 of the slide was made straight across that there was a tendency to drag the solution from the groove l2 as the slide was moved along the bar instead of leaving a test strip of uniform thickness throughout. To overcome this dificulty the cross member 23 f the slide was provided with a shallow arcuate recess 24' disposed above the groove l2 in the bar, see Fig. 5. In Fig. 6 we have shown a form of test strip 33 for gelatine solutions which has proved entirely satisfactory.

We have found that the gel temperatures obtained were reproducible and varied with the concentration,.age, and pH of the solution. Tests showed that the gel temperatures vary about -1 F. over a period of 7 to 11 minutes from thetime of coating, and a reading taken in this time range could be usedas the gel temperature. Below are iven the results of a seriesof tests'made with the method and apparatus set forth to point out how the threenoted variables, concentratiomage, and pH of-the solution affect :the gelation temperature of thegelatine solution.

I. Aseries to show the variation of the gel temperatures with gelatine concentration.

Waiting vtime vs, temperature F.)

7 min. 9min. 11min.

. G. gelatine no so 71.5-76.5 76 -73 I 18 49.5 so -s2.5 so -34 109. (go. Hi0:

no. so

Waiting time vs. temperature F.)

gelatine I 5 min 7 min. I 9 min. 11min.

HG SG HG SG 65 65 .-7 0.5 65 1-71 68.543 69 .73 1o 76 .0) 76 12 73 76.5 74.6-77 :77 76 77.5 14. 75. 5-79 76 .78.5 7.6 79.5 76.5e80

Note etrical-insists. I

III. The pH (hydrogen ion concentration) of a gelatine solution containing 10g. of gelatine per cc. of water was varied and the gel temperatures wereas follows:

pH 7 min. 9 min.

HG S G 73. 577. 5 76 78 This method of determining the gel temperatures of agelatine solution is quite accurate and in addition is a fast control method. As this method nearly eliminates the effect of time 1011 gelation, such as enters into the above noted bottle testing method, itis afar better control method than the latter. By knowingtwoof the three variables of age, concentrationandp I-I, it is valu able in checking the uniformity of gelatine batches to be sure that they are all alike and have the desired gel temperature which maybe prescribedby the limits of the chilling step available in a given coating machine. 4

The. steps necessary to the determination of the gelation temperature of a solution capableof sel i g a a i e tempc at rei .acqors an w th the od co sti ut ng th p esen invent o will now be outlined. The water supply to the test bar condensers is adjusted to obtain a de- Sider t m atur ad n along the ba whic willinclude thegela ion temperatu e of tir s lution to be tested. The bar should notbe used until al th m ters rema constan w th f r fire minutes. fio u ions fo tests 11 111 1 be in co apsi le tube W1lQB neck is threaded o t the t s ba slide. The slides andtubes fullof gtfii solution. should be, :kep,t .in :an oven p ior't test:so.;. hat the two wi lbe atthe coatin temperature .of the. solution. ;.T.he tube or .solution is screwed into the :proper slide and the slide placed ;on ;the bar at the warm end thereof.

By squeezing th tubeand moving the slide to-" ward the cold end of the bar a test strip of dope, or solution, is coated in the groove on, the bar. It should be pointed out that if solutions including solvents, and capable of being stripped from the test bar, are being tested, a bar with a narrow groove in a Slide giving a top strip of proper thickness is used for the deposition of the test strip. If, on the other hand, the solution being tested is a gelatine solution the bar with the shallow and wide groove is used along with a slide providing for no protective top strip.

After the proper waiting time (determined by the plateau time outlined above) the test strip, if it be a solution including solvents, is stripped off the test bar by raising a small portion of the cold end and pulling toward the warm end of the bar. The rate of pulling should beuniform, and a satisfactory rate has been found to be about seconds per foot. At some point the column of solution in the groove will stick and break. This point'is the stripping point and the temperature as indicated by the thermometers is the stripping, or gelation, temperature. If'the strip of solution being tested is a gelatine solution, instead of using a stripping technique to determine the point in a strip where the solution ceases to be a fluid and becomes a gel, the pins on the test comb are stuck into one edge of the strip in the groove and are all drawn laterally thereof simultaneously. If the pins leave a sharp edge groove in the strip that portion of the solution is gelled hard, that portion of the strip where the pins leave ragged grooves is gelled soft, and where no grooves are left by the pins the solution is still fluid. The temperature of the bar as read under these divisionsgives the gel temperature of the gelatine solution being considered.

It might be pointed out that the gelling of a solvent solution or an aqueous solution of gelatine may take place over a given temperature range rather than actually suddenly occurring at a given point. Therefore, in the above specification when the gelation temperature of a solvent solution is mentioned, that temperature at which the solution is sufficiently gelled to permit stripping from a film forming surface is referred to. On the other hand, when gelation temperature is mentioned in connection with solutions, such as aqueous solutions of gelatine, which are not capable of being stripped, the temperature at which such a solution shows a clean cut groove when scored by a pin, as above mentioned, is referred to. a r

While we have shown and described certain specific embodiments of our invention,--we are fully aware that many modifications of the same are possible. Our invention, therefore, is not to be limited to the precise details shown and described but is intended to cover all modifications coming within the scope of the appended claims.

'Having thus described our-invention what we claim is new and desire to secure by Letters'Patent of the United States is: r

1. The method of determining the gelation temperature of a liquid solution capable of gelling at a given temperature which comprises the steps of applying a uniform strip of said liquid solution along a support having a temperature gradient including said given temperature, determining the point on said support at which the deposited strip ceases to be a fluid and becomes a gel after remaining on said support for a'given time, and noting the temperature of the support at this point.

2. The method along said bar including said given temperature, applying auniformstrip'of said liquid solution along said support in'the direction of said gradient, determining the point on said bar at which the deposited solution ceases to be a fiuid'and becomes a gel after-remaining on said bariora given time, and noting the temperature ofthe. bar at this point. 1 V o 1' 3. The method of determining the gelation temperature. of a liquid solution capable of gelling at a given temperature which comprises the steps of applying a uniform strip of said solution along, a'support having a temperature gradient including said given temperature, then stripping said Strip from the support after it has remained thereon for a given time, starting with the end thereof on the lower temperature end of the support, until said strip sticksto said support, and determining the temperature of the support at the point where said strip first sticks thereto. 7 V

4. The method of determining the gelation temperature of a liquid solution capable of gelling at a given temperature which comprises the steps of applying 'a uniform strip of said solution along a support having a temperature gradient including said given temperature, and in such a way that that portion of the solution directly engaging the supp rt and immediately adjacent thereto is isolated from contact with the atmos: phere surrounding the support, then stripping said strip from the support after remaining thereon for a given time, starting with the end thereof on the lower temperature end of the sup port, until said strip sticks to the support, and determining the temperature of the supportlat the point where said strip first sticks thereto. 5. The method of determining the gelation temperature of a liquid solution capable of gelling at a given temperature which comprises the steps of applying a uniform strip of said solution in an elongated groove formed in a support hav-' ing a temperature gradient lengthwise of said groove and including said given temperature, iso lating that portion of the solution in said groove from air surrounding the support, then stripping said strip from, the support after remaining thereon for a given time, starting with' the end thereof on the lower temperature end' of the support, until said strip sticks in said groove, and determining the temperature of the support at the point where said strip first sticks in said groove. L

6. The method of determining the gelation temperature of a liquid'solution capable of gelling at a given temperature which comprises the steps of applying a uniform strip of said solution in an elongated groove formed in-a support having a temperature gradient lengthwise of said groove and includingsaid given temperature in such a way that the solution fills said groove and provides a top strip of substantial thickness over said groove to isolate the portion 'of material therein from air surrounding the support, then stripping said strip from the support afterre maining thereon fora given time, startingwith the end thereof onthe lower temperature end of of determining the gelation temperature of a liquid solution capable'of gene 1 ing at a given temperature which comprises'the; steps of heating one end of a bar of heat con-1 ductive material and cooling the other end there'- of to obtain a constant temperature gradient,

the support, until said strip sticks in said groove, and determining the temperature of the support at the point where said strip first sticks in said groove.

7. A device for determining the gelation temperature of a liquid solution capable of gelling at a given temperature, comprising an elongated bar composed of a heat conductive material and including a surface therealong onto which a uniform strip of the solution to be tested is adapted to be deposited, said surface provided with a groove extending therealong into which said solution is adapted to flow, means for heating one end of said bar and cooling the other end thereof to provide a temperature gradient therealong including the gelling temperature of said solution, and means for determining the temperature of said bar at successive points therealong in the direction of said groove.

8. A device for determining the gelation temperature of a liquid solution capable of gelling at a given temperature, comprising an elongated bar composed of a heat conductive material and including a surface therealong onto which a uniform strip of the solution to be tested is adapted to be deposited, said surface provided with a groove extending therealong into which said solution is adapted to flow, a carriage mounted on said bar to move therealong in the direction of said groove, means on said carriage for attaching a dispenser for said solution thereto whereby a uniform strip of the solution is applied to said surface as the carriage is moved along said bar, means for heating one end of said bar and cooling the other end thereof to provide a temperature gradient therealong including the gelling temperature of said solution, and means for determining the temperature of said bar at successive points therealong in the direction of said groove.

9. A device for determining the gellation temperature of a liquid solution capable of gelling at a given temperature, comprising an elongated bar composed of a heat conductive material and including a surface therealong onto Which a uniform strip of the solution to be tested is adapted to be deposited, said surface provided with a groove extending therealong into which said solution is adapted to flow, a carriage mounted on said bar to move therealong in the direction of said groove, means on said carriage for attaching a dispenser for said solution thereto whereby a uniform strip of the solution is applied to said surface as the carriage is moved along said bar, means for heating one end of said bar and cooling the other end thereof to provide a temperature gradient therealong including the gelling temperature of said solution, and a plurality of thermometers embedded in said bar at spaced intervals therealong in the direction of said groove for indicating the temperatures of said bar at different points therealong.

10. A device for determining the gelation temperature and stripping characteristics of a liquid solution capable of gelling at a given temperature, comprising an elongated stripping bar composed of a heat conductive material and including a surface therealong onto which a uniform strip of the solution to be tested is adapted to be deposited, said surface provided with a groove extending therealong into which said solution is adapted to flow, acarriage slidably mounted on said bar to move therealong in the direction of said groove, and including a portion adapted to slidably engage said grooved surface of the bar, said portion of the carriage provided with an elongated slot disposed above said groove, which is wider than said groove and has its bottom spaced from said surface, and means on said carriage for detachably connecting a dispenser for said solution thereto with its outlet in communication with said slot whereby a uniform strip of solution is adapted to be applied to said surface and the groove therein as the carriage is moved along said bar, means for heating one end of said bar and cooling the other end thereof to provide a temperature gradient therealong including the gelling temperature of said solution, and means on said bar for indicating the temperature of the same at successive points therealong in the direction of said groove.

11. A device for determining the gelation temperature and stripping characteristics of a liquid solution capable of gelling at a given temperature, comprising an elongated stripping bar composed of a heat conductive material and including a surface therealong onto which a uniform strip of the solution to be tested is adapted to be deposited, said surface provided with a groove extending therealong into which said solution is adapted to flow, a carriage slidably mounted on said bar to move therealong in the direction of said groove, and including a portion adapted to slidably engage said grooved surface of the bar, said portion of the carriage provided with an elongated slot disposed above said groove, which is wider than said groove and has its bottom spaced from said surface, and means on said carriage for detachably connecting a dispenser for said solution thereto with its outlet in communication with said slot whereby a uniform strip of solution is adapted to be applied to said surface and the groove therein as the carriage is moved along said bar, means for heating one end of said bar and cooling the other end thereof to provide a temperature gradient therealong including the gelling temperature of said solution, said last mentioned means including fluid condensers immersing opposite ends of said bar and having the temperature of the fluids regulated to give the desired temperature gradient, and means on said bar for indicating the temperature of the same at successive spaced points therealong in the direction of said groove.

CHARLES R. FORDYCE. HAROLD F. VIVIAN. 

